The present invention relates to rolling mills and more in particular to a vacuum roll mill stand.
1. Field of the Invention
The invention is preferably used where high-quality articles of exceptional purity are manufactured in vacuum or in an inert atmosphere from metals and alloys highly active chemically and of low ductility, for example, such as those based on tungsten, molybdenum, titanium, niobium.
Though the articles from such metals and alloys are usually manufactured in small quantities, they may greatly vary in type, size and shape, which necessitates frequent roll adjusting and changing operations to be carried out during operating process.
2. Description of the Prior Art
For example, there are known in the art vacuum rolling mills in which the mill stand and various roll adjustment mechanisms, fittings and spindles are housed within a vacuum chamber, with the mill drive being positioned externally thereof.
In the rolling mills of this type a vacuum chamber has a relatively large volume, which necessitates employment of a powerful vacuum system. To carry out the roll readjustment or changing operation, the vacuum chamber should be dismounted, this being very time-consuming.
There are also known vacuum roll mill stands in which a vacuum chamber is adapted solely for the accommodation of workrolls.
The vacuum chamber in the above roll mill stand is relatively small in size, whereas the system of vacuum sealing is rather complicated, especially so in the places at which the workrolls are introduced into the vacuum chamber. The vacuum system is rendered still more complicated and, consequently, less reliable in operation, in view of additional means installed at the roll necks and chocks to compensate for the leakage in the vacuum system due to take place during operation by reason of elastic bending of the workrolls. The changing of rolls is time- and labor-consuming operation, involving complete dismounting and subsequent mounting of the vacuum sealings, which are rather complicated in construction.
Another vacuum roll mill stand known in the prior art comprises a box-shaped housing which accommodates chocks carrying workrolls geared through the intermediary of spindles to a drive. The side walls of the housing are provided with ports for mounting and dismounting the workrolls therethrough. To establish vacuum in the interior of the roll housing, the ports are closed with covers having vacuum seals.
The cover positioned from the side of the mill drive is formed with a cavity adapted to accommodate spindles. The hermetically sealed chamber thus formed is brought in communication with a vacuum pumping means.
In order to perform the roll changing operation in the aforedescribed roll mill stand, it is necessary to remove the covers with vacuum seals, as well as the spindles, chocks and workrolls, and then to carry out the reassembly operation in reverse order, which takes up much time and labour. It particularly holds true for those instances where refractory and hard-to-work metals and alloys are to be rolled with the resultant high rate of wear of the workrolls. This, in turn, demands frequent changing of rolls, the disadvantage adversely affecting production efficiency of a rolling mill.
The roll pass in the prior-art rolling mills is formed by two workrolls. Rolling in such roll passes fails to ensure a favourable reduction schedule necessary for plastic deformation of hard-to-work metals and alloys, which makes it impossible to produce a wide variety of shaped sections from such metals.